DESCRIPTION: (Adapted from the application) The common late life neurodegenerative diseases (ND), Alzheimer s disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis, are characterized by the gradual death of specific neurona1 populations. Shared cell level pathophysiology may include: 1) bioenergetic dysfunction, 2) oxidative stress, 3) perturbed calcium homeostasis, and 4) glutamate excitotoxicity. A combination of these factors likely contributes to neuronal programmed cell death (apoptosis), so defining the etiology and interactions of these mechanisms could provide therapeutic leads for ND. This project concentrates on bioenergetic electron transport chain (ETC) dysfunction in ND. Mitochondrial ETC defects clearly exist in AD and PD, but questions regarding their origin and pathologic significance remain unanswered. Objectives are to learn if ETC dysfunction is a common theme in ND, whether ETC dysfunction drives or is driven by other degenerative mechanisms, and to what extent ETC defects contribute to apoptosis. Development of a controlled system in which the only variable is ETC-defective mitochondria derived from specific ND will facilitate a direct, systematic exploration of these issues. The transfer of human mitochondrial DNA (mtDNA) from AD and PD subjects to mtDNA-depleted culturable cells results in the creation of cytoplasmic hybrids (cybrids) that express the respective ETC defects associated with these diseases. Other genetic and environmental factors remain under the investigator's control. Pilot studies indicate biochemical assays of cybrids can help determine: 1) whether mtDNA mutations contribute to ETC defects in particular ND, 2) the extent to which ETC defects contribute to oxidative stress in ND, 3) the extent to which ETC defects impair calcium homeostasis in ND, 4) whether ETC defects affect excitotoxicity thresholds in ND, and 5) how oxidative stress, calcium mishandling, and excitotoxicity conversely impact upon the ETC in ND.